This invention relates to fault diagnosis of an evaporative emission control system which prevents fuel evaporating gas from leaking to the atmosphere.
JP-A-H7-317611 published by the Japanese Patent Office in 1995 discloses a diagnosis of an evaporative emission control system. In this system, an absolute pressure sensor is installed midway in a passage which connects a fuel tank and a canister, and the atmospheric pressure measured by an atmospheric pressure sensor separately installed outside the system is set as a reference pressure. Faults of the evaporative emission control system are diagnosed based on the differential pressure between the reference pressure and the pressure in a passage.
However, in the conventional fault diagnosis, in addition to the absolute pressure sensor in the system, it is necessary to provide an atmospheric pressure sensor separately outside the system.
It is therefore an object of this invention to diagnose a fault of an evaporative emission control system from the measurement result of an absolute pressure sensor without providing an absolute pressure sensor outside the system.
In order to achieve above object, this invention provides a fuel evaporative emission control system of an engine comprising a fuel tank, a passage connecting the fuel tank and an intake passage of the engine, a canister provided in the passage, which adsorbs fuel evaporating gas vaporized in the fuel tank, a purge valve installed between the intake passage and the canister, a sensor which is provided between the purge valve and the fuel tank and detects the pressure in the passage, and a controller functioning to detect the pressure in the passage before engine startup as an atmospheric pressure.
According to an aspect of the present invention, this invention provides a fuel evaporative emission control system of an engine, comprising a fuel tank, a passage connecting the fuel tank and an intake passage of the engine, a canister provided in the passage, which adsorbs fuel evaporating gas vaporized in the fuel tank, a purge valve installed between the intake passage and the canister, a sensor which is provided between the purge valve and the fuel tank and detects the pressure in the passage, and a controller functioning to detect the pressure in the passage before engine startup as a first pressure, detect the pressure in the passage after engine startup as a second pressure, compute the pressure difference between the first pressure and the second pressure, and determine a fault of the purge valve based on the pressure difference.